1. Field of the Invention
The present invention relates to an image defect correction apparatus and method, and a program therefor. More particularly, the present invention relates to an image defect correction apparatus for correcting image defect components contained in luminance signals output in a predetermined order from two-dimensionally arranged light-receiving elements via a plurality of vertical charge coupled devices and at least one horizontal charge coupled device, an image defect correction method applied to the image defect correction apparatus, and a program for causing a computer to execute the image defect correction method.
2. Description of the Related Art
In recent years, image pickup apparatuses such as home video cameras and digital still cameras have been in wide spread use. Most of them include a solid-state image pickup device comprised of two-dimensionally arranged light-receiving elements, a plurality of vertical CCDs (charge coupled devices), and a horizontal CCD (instead a plurality of horizontal CCDs can be included). The vertical CCDs vertically extend along vertical columns of light-receiving elements. The horizontal CCD horizontally extends and is connected to respective one ends of the vertical CCDs. Via the vertical and horizontal CCDs, luminance signals are taken out from the light-receiving elements in a predetermined order.
An image pickup device of the above kind has several hundred thousand to several million pixels and is formed on a semiconductor wafer, which ordinarily includes a certain level of substrate deficit (point defect).
Generally, the luminance signal at the pixel corresponding to a point defect is high in luminance all the time irrespective of the amount of light received by the light-receiving element including the point defect, and does not affect luminance signals at adjacent pixels. Hence, only one point on the resulting image becomes white in color.
To overcome the above described problem caused by point defects, a known image defect correction apparatus stores data indicating the position of a defective pixel in a solid-state image pickup device and the defective component level of output signal at the defective pixel, and performs defect correction in accordance with electric charge accumulation time at the defective pixel (see, for example, Japanese Patent Laid-open No. 1-103375 matured into Japanese Patent No. 2565261).
Since luminance signals are usually shifted in a vertical CCD and output therefrom, when there is a point defect in the vertical CCD which the luminance signals pass through, all the luminance signals are affected by the point defect. Specifically, the intensities of all the luminance signals output from one vertical pixel array via the vertical CCD including the point defect increase by amounts corresponding to time periods required for the signals to pass through the defect. The luminance signals from the vertical pixel array are higher in luminance than those attained when there is no defect in the CCD, and as a result, a white vertical line is formed on the resulting image.
To eliminate such a problem due to a point defect in a vertical CCD, an image defect correction apparatus has been proposed (see, for example, Japanese Patent Laid-open No. 2004-364266), which subtracts an average value of luminance signals detected by a light shielding portion or a vertical dummy portion of a solid-state image pickup device from each of luminance signals output from a vertical CCD including a point defect.
However, the above described image defect correction apparatus is merely adapted to a case where there is only one point defect at the maximum in one vertical CCD.
If, for example, there are 10 point defects in the entire vertical CCDs of a solid-state image pickup device having 3000 pixels in the horizontal direction, the probability of occurrence of a plurality of point defects in one vertical CCD is represented as follows:
Probability=1−(probability of occurrence of not more than one point defect in one vertical CCD)=1−PERMUT(3000,10)/(3000^10)≈0.015=1.5%, where PERMUT(Na, Nb) represents the number of permutation with Nb elements chosen from Na elements.
As explained above, the probability of presence of a plurality of point defects in one vertical CCD is not rare. In that case, the conventional image defect correction apparatus cannot make less prominent a white vertical line.